Preparation of chlorofluorosilanes



Patented Mar. 5, 1946 UNITED s'm'ras Pm PREPARATION or'omonorwonosmanasJulian w. mu, Richard 'v. Lindsey,'Jr., mam

ard H. Wiley, Wilmington, Del.,' 'assignors to E. I. du Pont de Nemmington, DeL,

ours &'.Company,- Wi l-" a corporation of-Delaware f No Drawing.Application April 10, 1944,

' Serial No. 530,398 V Claims. (01. 23 -14) This invention relates to animproved process for the preparation of chlorofluorosilanes.

This invention has as an object the production of chlorofluorosilanes. Afurther object is the preparation of dichlorodifiuorosilane. Additionalobjects will become apparent from an examination of the followingdescription and claims.

These and other objects and advantages are accomplished by the hereindescribed invention which broadly comprises heating a compound anewithsilicon-tetrachloride, it is applicable to other combinations ofreactants. For example,

having the general formula SiClaX, wherein X is 7 an atom selected fromthe group consisting of chlorine and fluorine atoms, with a compoundhaving the general formula SiXF's, wherein X is an atom selectedfrom thefluorine and chlorine atoms.

The following examples, in which proportions group consisting of aregiven in parts by weight, are given for illustrative purposes and arenot intended to place any restrictions on the herein describedinvention:

Example I Two hundred fifty-seven parts of silicon tetrafluoride isbubbled through 272 parts of silicon tetrachloride heated to about 45C.v and there'- sultant mixture of gases about 600 C. These efliuentgases are passed through a vertical condenser maintained at -30 C.Trichlorofluorosilane and unchanged silicon tetrachloride are recycledby returning the condensate directly to the vessel containing thesilicon tetrachloride. The gaseous products which pass through thecondenser are collected in a trap cooled with a mixture of solid carbondioxide and acetone. Q distilled to obtain 102 parts oftrifluorochlorosil- The product is fractionally ane (B. P. -70 C.), 282parts of dichlorodifluorosilane (B. P. -32 C.) and 13 parts oftrichlorofluorosilane (B. P. 12 C.)

Example II trichlorofluorosilane and can be reacted to obtain additionaldifluorodichlorpsilane Thus, by proper choice of operatingconditions,i.'e.,' reactants, vaporizing temperature, and condensingtemperature, and recycling all but the desired silicon halide, anydesired chlorofiuorosilane can be obtained as the major product. 7

The reactions of silicon tetrachloride with silicon tetrafluoride, ofsilicon tetrachloride with chlorotrifluorosilane, oftrichlorofluorosilane with is passed through a glass .tube packed withbroken porous plate heated to Using a procedure similar to thatdescribed in the preceding example, 169 parts of the chloro-.trifluorosilane is biibbled through 24 parts of silicon tetrachlorideand the resultant mixed gases passed through the glass tube maintainedat a temperature of 500 C.. Upon distillation of the silicontetrafluoride and of trichlorofluorosilane with chlorotrifluorosilane,respectively, maybe The preparation of the chlorofluorosilane is usuallycarried out at a temperature within the range of from about 250 C.to-900" C., or even at higher temperatures. For best results,temperatures within the range of from 350 C. to 650" are used. Attemperatures below 350 C. the rate of reaction is low; whereas operatingat temper.

atures above 650 C. does notresult in any appreciable increase in yieldsof the chlorofluorosilanes, but does increase costs. I

The reaction can'be carried out in any suitable reaction vesselconstructed of glass, quartz, steel, copper or iron. Other materials inaddition to porous plate can be used'as contact surfaces in the reactionvessel. These include porcelain, quartz, glass, metal,'etc. In someinstances, particularly at the higher reaction temperatures-itis'advantageous to omit the contact surfaces.

The products obtained by the practice of this invention are useful for anumber of commercial purposes. They areparticularly valuable asintermediates for the preparation or a large number or'organic As manyapparently widely diflerent embodiments of this invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specificembodimentsthereof except as de-' fined in the appended claims. 7

Having described the present invention, the following is claimed as newand-useful:

1. The process for obtaining chlorofluorosiloFFicEf jchlorotrifluorosilane and inorganic compounds of siliones, in! the atomselected from the group consisting of chlorine and fluorine atoms, witha compound having the general tormu1a SiXFz, wherein x is an atomselected from the groupconsisting chlorine atoms. V

2'. The process according toclaim 1 wherein which comprises heating acompound hav- 'th'e reactionis eflected at a temperature within therange of Irom 350 C to 650 C.

8. The process for obtaining chlorofluorosilaneawhich'comprises heatinga mixture of silitesmperature within the range of from 350 C. to 6 0 C.

oi fluorine and con tetrachloride and silicon tetrafluoride-to a,

a 4. The process for obtaining dichiorodifluoro general formula, SiClaX,wherein x is an silane, which comprises heating a mixture 0! silicontetrachloride and silicon tetrafluorlde to a temperature within therange or from 350 Otto 650 0., cooling'the resultant emuent gases toremove the dichlcrodifluorosilane, and recycling the residual gasesthrou'ah' -the"reaction mixture.

5. The process for obtai -.dichl orodiiluoro- 'silane, which comprisesheating a mixture of chlorotrifluorosilane and trichlorofluorosilane toa temperature within the range of from 350 C. to

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